I'm confused about how someone can consider using a hash to "encode" a URL and then worry about collisions without realizing that collisions can only come about because a hash is non-reversible. Lossy compression implies a loss of information, which in the case of URLs seems kinda bad. I'm also more than a little bit surprised that folks didn't just know that it has typically been an incrementing counter, but maybe I just started seeing tinyurl links early enough in its life that it was obvious. But geez, I'm not even a web guy.